The present invention relates generally to drills and more particularly to drills of the twist or spiral type having a cutting edge that can be sharpened or resharpened by machine grinding.
Twist or spiral drills have been developed for used in many types of drilling applications. See, for example, U.S. Patent (Karafillis et al), issued Dec. 8, 1998. Twist drills typically have a cylindrical body, a pair of helical or spiral grooves or flutes formed in the outer peripheral surface of the body and a pair of lands each disposed between the pair of flutes. Each flute has a wall or face that is usually concavely shaped. The portion of the wall of each flute facing in the direction of rotation of the drill body (the cutting face) terminates at its forward end (the drill point) in a cutting edge or lip.
Twist drills can be used in heavy-duty operations such as drilling materials used in aerospace or jet engine components. The materials used in these components are often formed from high temperature alloys such as nickel-based alloys. The cutting edge of the drill used in drilling such high temperature alloys can become dull over time and can require regrinding to sharpen the cutting edge. Also, because of the stress that the cutting edge is subjected to during drilling, the cutting edge can become chipped or fractured, thus also requiring regrinding of the drill.
To lengthen the time before regrinding of the cutting edge of the drill is required and to minimize the occurrence of chipping or fractures, the cutting edge of the drill can be honed across its surface. Previously, this honed edge has been manually created by using a diamond file to form a planar surface in the cutting edge. However, manual honing requires special skills for the one carrying it out and does not provide a uniform and consistent honed surface from drill to drill. In particular, it is difficult to manually hone a relatively straight, planar surface in the cutting edge. It is especially difficult to make these manually honed edges consistent for each of the pair of cutting edges in a standard twist drill. This can again make the cutting edges more prone to chipping or fracture because of the uneven stress that the cutting edges are subjected to during the drilling operation.
In order to make the honed surface in the cutting edge straighter and more consistent from drill to drill, it would be desirable to form this honed surface in the cutting edge by machine grinding, especially by using a computerized numerically controlled (CNC) grinding machine. However, machine grinding of the cutting edge to formed this honed surface (referred to hereafter as a xe2x80x9ccutting landxe2x80x9d) can be difficult, especially since there are typically slight inaccuracies in the flute spacing of the drill. As a result, CNC machine grinding of this cutting land into the cutting edge of the drill within tightly controlled dimensions is typically not possible.
Accordingly, it would desirable, therefore, to provide a twist or spiral drill that has a cutting land in the cutting edge that can be formed uniformly and consistently from drill to drill by machine grinding, preferably using a CNC grinding machine, even if there are slight inaccuracies in the flute spacing of the drill.
The present invention relates to a drill having a cutting end. The drill includes a body and at least one flute formed in the body. A dub face is formed adjacent a surface of the flute and proximate the cutting end of the drill. The dub face has a substantially planar surface portion. The drill includes a cutting land, and a cutting edge associated with the cutting land. The cutting land has a substantially planar surface over at least a portion thereof, the planar surface portion of the cutting land being connected at an edge to the planar surface portion of the dub face. The cutting edge is spaced from the dub face by the cutting land.
The present invention further relates to a method for machine grinding the cutting edge of the drill to form the cutting land. In this method, the dub face is formed in a surface of the flute of the drill proximate the cutting end of the drill, the dub face having a substantially planar surface over at least a portion thereof, the planar surface portion of the dub face being connected at an edge to the surface of the flute. After the dub face is formed, a drill cutting edge and cutting land are machine ground to form a cutting land having a substantially planar surface over at least a portion thereof, such that the planar surface portion of the cutting land is connected at an edge to the planar surface portion of the dub face, and such that the cutting edge is spaced from the dub face by the cutting land.
Forming the dub face in the surface of the flute of the drill allows the cutting land to be formed in association with cutting edge by machine grinding, including CNC machine grinding, uniformly and consistently from drill to drill. As a result, the cutting edge of the drill of the present invention is less prone to chipping or fracturing when used in drilling operations involving high temperature metal alloys and can be sharpened or resharpened uniformly and consistently by machine grinding. Indeed, the present invention allows the cutting land to be repeatedly formed uniformly and consistently, including CNC machine grinding, within tightly controlled dimensions, even if there are slight inaccuracies in the flute spacing of the drill.